1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to circuits for converting analog data to digital data.
2. Related Art
Digital signal processing has been proven to be very efficient in handling and manipulating large quantities of data. There are many products that are in common use such as wireless devices, digital cameras, motor controllers, automobiles, and toys, to name a few, that rely on digital signal processing to operate. Many of these products continuously receive information that is monitored and used to produce adjustments to the system thereby maintaining optimum performance. The data is often an analog signal that must be converted to a representative digital signal. For example, light intensity, temperature, revolutions per minute, air pressure, and power are but a few parameters that are often measured. Typically, an analog to digital (A/D) converter is the component used to convert an analog signal to a digital signal. In general, the conversion process comprises periodically sampling the analog signal and converting each sampled signal to a corresponding digital signal.
Many applications require the analog to digital converter(s) to sample at high data rates, operate at low power, and provide high resolution. These requirements are often contradictory to one another. Furthermore, cost is an important factor that directly correlates to the amount of semiconductor area needed to implement a design. One type of analog to digital converter that has been used extensively is a redundant signed digit (RSD) analog to digital converter. The RSD analog to digital converter typically comprises one or more RSD stages and a sample/hold circuit. In one embodiment, a sampled voltage is compared against a high reference voltage and a low reference voltage. The result of the comparison is used to determine 1.5 bits from the RSD stage. A residue voltage is then generated that is 2 times the sampled voltage plus or minus the reference voltage. The residue voltage is then provided to another RSD stage or fed back in a loop to continue the conversion process to extract bits until the least significant bit is generated.